A microfiche appendix is contained in U.S. application Ser. No. 08/869,276, herein incorporated by reference.
This invention relates generally to observing fluorescence signals resulting from hybridization in conjunction with the polymerase chain reaction. More specifically, the present invention relates to observing hybridization with fluorescence during and/or immediately after PCR and using this information for product identification, sequence alteration detection, and quantification.
The polymerase chain reaction (PCR) is fundamental to molecular biology and is the first practical molecular technique for the clinical laboratory. Despite its usefulness and popularity, current understanding of PCR is not highly advanced. Adequate conditions for successful amplifications must be found by trial and error and optimization is empirical. Even those skilled in the art are required to utilize a powerful technique without a comprehensive or predictive theory of the process.
PCR is achieved by temperature cycling of the sample, causing DNA to denature (separate), specific primers to attach (anneal), and replication to occur (extend). One cycle of PCR is usually performed in 2 to 8 min, requiring 1 to 4 hours for a 30-cycle amplification. The sample temperature response in most PCR instrumentation is very slow compared to the times required for denaturation, annealing, and extension. The physical (denaturation and annealing) and enzymatic (extension) reactions in PCR occur very quickly. Amplification times for PCR can be reduced from hours to less than 15 min. Incorporated herein by reference in their entireties are each of the following individual applications, which disclose such a rapid cycling system: U.S. application Ser. No. 08/818,267, filed Mar. 17, 1997, entitled Method for Detecting the Factor V Leiden Mutation, which is a continuation-in-part of U.S. patent application Ser. No. 08/658,993, filed Jun. 4, 1996, entitled System And Method For Monitoring PCR Processes, which is a continuation-in-part of U.S. patent application Ser. No. 08/537,612, filed Oct. 2, 1995, entitled Method For Rapid Thermal Cycling of Biological Samples, which is a continuation-in-part of U.S. patent application Ser. No. 08/179,969, filed Jan. 10, 1994, (now U.S. Pat. No. 5,455,175), entitled Rapid Thermal Cycling Device, which is a continuation-in-part of U.S. patent application Ser. No. 07/815,966 filed Jan. 2, 1992, (now abandoned) entitled Rapid Thermal Cycling Device which is a continuation-in-part of U.S. patent application Ser. No. 07/534,029 filed Jun. 4, 1990, (now abandoned) entitled Automated Polymerase Chain Reaction Device. The copending U.S. application filed in the U.S. Patent and Trademark Office on Jun. 4, 1997, entitled System and Method for Carrying Out and Monitoring Biological Processes as Ser. No. 08/869,275 and naming Carl T. Wittwer, Kirk M. Ririe, Randy P. Rasmussen, and David R. Hillyard as applicants, is also hereby incorporated by reference in its entirety. Rapid cycling techniques are made possible by the rapid temperature response and temperature homogeneity possible for samples in high surface area-to-volume sample containers such as capillary tubes. For further information, see also: C. T. Wittwer, G. B. Reed, and K. M. Ririe, Rapid cycle DNA amplification, in K. B. Mullis, F. Ferre, and R. A. Gibbs, The polymerase chain reaction, Birkhauser, Boston, 174-181, (1994). Improved temperature homogeneity allows the time and temperature requirements of PCR to be better defined and understood. Improved temperature homogeneity also increases the precision of any analytical technique used to monitor PCR during amplification.
Fluorimetry is a sensitive and versatile technique with many applications in molecular biology. Ethidium bromide has been used for many years to visualize the size distribution of nucleic acids separated by gel electrophoresis. The gel is usually transilluminated with ultraviolet light and the red fluorescence of double stranded nucleic acid observed. Specifically, ethidium bromide is commonly used to analyze the products of PCR after amplification is completed. Furthermore, EPA 0 640 828 A1 to Higuchi and Watson, hereby incorporated by reference, discloses using ethidium bromide during amplification to monitor the amount of double stranded DNA by measuring the fluorescence each cycle. The fluorescence intensity was noted to rise and fall inversely with temperature, was greatest at the annealing/extension temperature (50xc2x0 C.), and least at the denaturation temperature (94xc2x0 C.). Maximal fluorescence was acquired each cycle as a measure of DNA amount. The Higuchi and Watson application does not teach using fluorescence to monitor hybridization events, nor does it suggest acquiring fluorescence over different temperatures to follow the extent of hybridization. Moreover, Higuchi and Watson fails to teach or suggest using the temperature dependence of PCR product hybridization for identification or quantification of PCR products.
The Higuchi and Watson application, however, does mention using other fluorophores, including dual-labeled probe systems that generate flourescence when hydrolyzed by the 5xe2x80x2-exonuclease activity of certain DNA polymerases, as disclosed in U.S. Pat. No. 5,210,015 to Gelfand et al. The fluorescence observed from these probes primarily depends on hydrolysis of the probe between its two fluorophores. The amount of PCR product is estimated by acquiring fluorescence once each cycle. Although hybridization of these probes appears necessary for hydrolysis to occur, the fluorescence signal primarily results from hydrolysis of the probes, not hybridization, wherein an oligonucleotide probe with fluorescent dyes at opposite ends thereof provides a quenched probe system useful for detecting PCR product and nucleic acid hybridization, K. J. Livak et al., 4 PCR Meth. Appl. 357-362 (1995). There is no suggestion of following the temperature dependence of probe hybridization with fluorescence to identify sequence alterations in PCR products.
The specific hybridization of nucleic acid to a complementary strand for identification has been exploited in many different formats. For example, after restriction enzyme digestion, genomic DNA can be size fractionated and hybridized to probes by Southern blotting. As another example, single base mutations can be detected by xe2x80x9cdot blotsxe2x80x9d with allele-specific oligonucleotides. Usually, hybridization is performed for minutes to hours at a single temperature to achieve the necessary discrimination. Alternately, the extent of hybridization can be dynamically monitored while the temperature is changing by using fluorescence techniques. For example, fluorescence melting curves have been used to monitor hybridization. L. E. Morrison and L. M. Stols, Sensitive fluorescence-based thermodynamic and kinetic measurements of DNA hybridization in solution, 32 Biochemistry 3095-3104, 1993). The temperature scan rates are usually 10xc2x0 C./hour or less, partly because of the high thermal mass of the fluorimeter cuvette.
Current methods for monitoring hybridization require a lot of time. If hybridization could be followed in seconds rather than hours, hybridization could be monitored during PCR amplification, even during rapid cycle PCR. The many uses of monitoring hybridization during PCR, as will be fully disclosed herein, include, product identification and quantification, sequence alteration detection, and automatic control of temperature cycling parameters by fluorescence feedback
The prior art, as explained above, carries out temperature cycling slowly and empirically. When analysis of PCR products by hybridization is needed, additional time consuming steps are required. Thus, it would be a great advance in the art to provide methods for monitoring hybridization during PCR and analyzing the reaction while it is taking place, that is, during or immediately after temperature cycling without manipulation of the sample. By monitoring hybridization during PCR, the underlying principles that allow PCR to work can be followed and used to analyze and optimize the reaction during amplification.
It is an object of the present invention to provide a double-strand-specific DNA dye for monitoring product hybridization during PCR.
It is another object of the invention to provide a system for identifying PCR-amplified products by their fluorescence melting curves.
It is also an object of the invention to provide a method for improving the sensitivity of PCR quantification with double-strand-specific DNA dyes.
It is still another objection of the invention for determining the amount of specific product amplified by PCR by melting curves to correct for nonspecific amplification detected with the double-strand-specific DNA dye.
It is a further object of the invention to provide a method of relative quantification of different PCR products with double-strand-specific dyes.
It is yet another object of the invention to provide a method of product quantification by the reannealing kinetics of the product in the presence of a double-strand-specific DNA dye.
It is a still further object of the invention to provide a novel resonance energy transfer pair to monitor primer and/or probe hybridization.
It is still another object of the invention to provide a method of product quantification by the reannealing kinetics of a probe to the product using a resonance energy transfer pair.
It is also an object of the present invention to provide a method to determine initial template copy number by following the fluorescence of a hybridization probe or probes each cycle during PCR amplification.
It is another object of the invention to provide a system for homogeneous detection of PCR products by resonance energy transfer between two labeled probes that hybridize internal to the PCR primers.
It is still another object of the invention to provide a system for homogeneous detection of PCR products by resonance energy transfer between one labeled primer and one labeled probe that hybridizes internal to the PCR primers.
It is yet another object of the invention to provide a system for detection of sequence alterations internal to PCR primers by resonance energy transfer and probe melting curves.
It is a further object of the invention to provide a system for relative quantification of different PCR products by probe melting curves.
It is yet another object of the invention to provide methods to determine the initial template copy number by curve fitting the fluorescence vs cycle number plot.
It is still another object of the invention to provide a system and method for performing PCR rapidly and also continuously monitoring the reaction and adjusting the reaction parameters while the reaction is ongoing.
It is another object of the invention to replace the nucleic acid probes by synthetic nucleic acid analogs or derivatives, e.g. by peptide nucleic acids (PNA), provided that they can also be labeled with fluorescent compounds.
These and other objects and advantages of the invention will become more fully apparent from the description and claims which follow, or may be learned by the practice of the invention.
The present invention particularly decreases the total time required for PCR amplification and analysis over prior art techniques while at the same time allowing the option of significantly increasing the quality of the reaction by optimizing amplification conditions.
The present invention provides methods and applications for continuous fluorescence monitoring of DNA amplification. Required instrumentation combines optical components with structures to provide rapid temperature cycling to continuously monitor DNA amplification by a variety of different fluorescence techniques. In one illustrative embodiment, fluorescence is acquired continuously from a single sample or alternately from multiple samples on a rotating carousel with all of the samples being simultaneously subjected to rapid thermal cycling. Further information on associated instrumentation can be found in the U.S. patent applications referenced above.
In accordance with one aspect of the present invention, fluorescence during DNA amplification was monitored by: 1) the double strand-specific dye SYBR Green I, and 2) resonance energy transfer of fluorescein to Cy5(trademark) or Cy5.5(trademark) with hybridization probes. Fluorescence data acquired once per cycle allow quantification of initial template copy number.
Furthermore, in contrast to measuring fluorescence once per cycle, embodiments of the present invention are disclosed which monitor temperature, time and fluorescence continuously throughout each cycle thus producing a 3-dimensional spiral. This 3-dimensional spiral can be reduced to temperature vs. time, fluorescence vs. time, and fluorescence vs. temperature plots. Fluorescence vs. temperature plots of the fluorescence from hybridization probes can be used to detect sequence alterations in the product. These sequence alterations may be natural, as in mutations or polymorphisms, or artificial, as in an engineered alternative template for quantitative PCR.
In accordance with another aspect of the present invention, fluorescence monitoring is used to acquire product melting curves during PCR by fluorescence monitoring with double-strand-specific DNA specific dyes. Plotting fluorescence as a function of temperature as the thermal cycler heats through the dissociation temperature of the product gives a PCR product melting curve. The shape and position of this DNA melting curve is a function of GC/AT ratio, length, and sequence, and can be used to differentiate amplification products separated by less than 2xc2x0 C. in melting temperature. Desired products can be distinguished from undesired products, including primer dimers. Analysis of melting curves can be used to extend the dynamic range of quantitative PCR and to differentiate different products in multiplex amplification. Using double strand dyes, product denaturation, reannealing and extension can be followed within each cycle. Continuous monitoring of fluorescence allows acquisition of melting curves and product annealing curves during temperature cycling.
The present invention provides reagents and methods for rapid cycle PCR with combined amplification and analysis by fluorescence monitoring in under thirty minutes, more preferably in under fifteen minutes, and most preferably in under ten minutes.
A method for analyzing a target DNA sequence of a biological sample comprises
amplifying the target sequence by polymerase chain reaction in the presence of two nucleic acid probes that hybridize to adjacent regions of the target sequence, one of the probes being labeled with an acceptor fluorophore and the other probe labeled with a donor fluorophore of a fluorescence energy transfer pair such that upon hybridization of the two probes with the target sequence, the donor and acceptor fluorophores are within 25 nucleotides of one another, the polymerase chain reaction comprising the steps of adding a thermostable polymerase and primers for the targeted nucleic acid sequence to the biological sample and thermally cycling the biological sample between at least a denaturation temperature and an elongation temperature;
exciting the biological sample with light at a wavelength absorbed by the donor fluorophore and detecting the emission from the fluorescence energy transfer pair.
A method for analyzing a target DNA sequence of a biological sample comprises
amplifying the target sequence by polymerase chain reaction in the presence of two nucleic acid probes that hybridize to adjacent regions of the target sequence, one of the probes being labeled with an acceptor fluorophore and the other probe labeled with a donor fluorophore of a fluorescence energy transfer pair such that upon hybridization of the two probes with the target sequence, the donor and acceptor fluorophores are within 25 nucleotides of one another, the polymerase chain reaction comprising the steps of adding a thermostable polymerase and primers for the targeted nucleic acid sequence to the biological sample and thermally cycling the biological sample between at least a denaturation temperature and an elongation temperature;
exciting the sample with light at a wavelength absorbed by the donor fluorophore; and
monitoring the temperature dependent fluorescence from the fluorescence energy transfer pair.
A method of real time monitoring of a polymerase chain reaction amplification of a target nucleic acid sequence in a biological sample comprises
(a) adding to the biological sample an effective amount of two nucleic acid primers and a nucleic acid probe, wherein one of the primers and the probe are each labeled with one member of a fluorescence energy transfer pair comprising an acceptor fluorophore and a donor fluorophore, and wherein the labeled probe hybridizes to an amplified copy of the target nucleic acid sequence within 15 nucleotides of the labeled primer;
(b) amplifying the target nucleic acid sequence by polymerase chain reaction;
(c) illuminating the biological sample with light of a selected wavelength that is absorbed by said donor fluorophore; and
(d) detecting the fluorescence emission of the sample.
An improved method of amplifying a target nucleic acid sequence of a biological sample comprises
(a) adding to the biological sample an effective amount of a nucleic-acid-binding fluorescent entity;
(b) amplifying the target nucleic acid sequence using polymerase chain reaction, comprising thermally cycling the biological sample using initial predetermined temperature and time parameters, and then
(i) illuminating the biological sample with a selected wavelength of light that is absorbed by the fluorescent entity during the polymerase chain reaction;
(ii) monitoring fluorescence from the sample to determine the optimal temperature and time parameters for the polymerase chain reaction; and
(iii) adjusting the initial temperature and time parameters in accordance with the fluorescence.
In one illustrative embodiment, the fluorescent entity comprises a double strand specific nucleic acid binding dye, and in another illustrative embodiment the fluorescent entity comprises a fluorescently labeled oligonucleotide probe that hybridizes to the targeted nucleic acid sequence.
A method for detecting a target nucleic acid sequence of a biological sample comprises
(a) adding to the biological sample an effective amount of a pair of oligonucleotide probes that hybridize to the target nucleic acid sequence, one of the probes being labeled with an acceptor fluorophore and the other probe labeled with a donor fluorophore of a fluorescence energy transfer pair, wherein an emission spectrum of the donor fluorophore and an absorption spectrum of the acceptor fluorophore overlap less than 25%, the acceptor fluorophore has a peak extinction coefficient greater than 100,000 Mxe2x88x921 cmxe2x88x921 and upon hybridization of the two probes, the donor and acceptor fluorophores are within 25 nucleotides of one another;
(b) illuminating the biological sample with a selected wavelength of light that is absorbed by said donor fluorophore; and
(c) detecting the emission of the biological sample. An illustrative resonance energy transfer pair comprises fluorescein as the donor and Cy5 or Cy5.5 as the acceptor.
A method of real time monitoring of a polymerase chain reaction amplification of a target nucleic acid sequence in a biological sample comprises
amplifying the target sequence by polymerase chain reaction in the presence of two nucleic acid probes that hybridize to adjacent regions of the target sequence, one of the probes being labeled with an acceptor fluorophore and the other probe labeled with a donor fluorophore of a fluorescence energy transfer pair such that upon hybridization of the two probes with the target sequence, the donor and acceptor fluorophores are within 25 nucleotides of one another, the polymerase chain reaction comprising the steps of adding a thermostable polymerase and primers for the targeted nucleic acid sequence to the biological sample and thermally cycling the biological sample between at least a denaturation temperature and an elongation temperature;
exciting the biological sample with light at a wavelength absorbed by the donor fluorophore and detecting the emission from the biological sample; and
monitoring the temperature dependent fluorescence from the fluorescence energy transfer pair.
A method of real time monitoring of a polymerase chain reaction amplification of a target nucleic acid sequence in a biological sample comprises
amplifying the target sequence by polymerase chain reaction in the presence of SYBR(trademark) Green I, the polymerase chain reaction comprising the steps of adding a thermostable polymerase and primers for the targeted nucleic acid sequence to the biological sample and thermally cycling the biological sample between at least a denaturation temperature and an elongation temperature;
exciting the biological sample with light at a wavelength absorbed by the SYBR(trademark) Green I and detecting the emission from the biological sample; and
monitoring the temperature dependent fluorescence from the SYBR(trademark) Green I. Preferably, the monitoring step comprises determining a melting profile of the amplified target sequence.
A method for analyzing a target DNA sequence of a biological sample comprises
(a) adding to the biological sample an effective amount of two nucleic acid primers and a nucleic acid probe, wherein one of the primers and the probe are each labeled with one member of a fluorescence energy transfer pair comprising an acceptor fluorophore and a donor fluorophore, and wherein the labeled probe hybridizes to an amplified copy of the target nucleic acid sequence within 15 nucleotides of the labeled primer;
(b) amplifying the target nucleic acid sequence by polymerase chain reaction;
(c) illuminating the biological sample with light of a selected wavelength that is absorbed by said donor fluorophore and detecting the fluorescence emission of the sample. In another illustrative embodiment, the method further comprises the step of monitoring the temperature dependent fluorescence of the sample, preferably by determining a melting profile of the amplified target sequence.
A method of detecting a difference at a selected locus in a first nucleic acid as compared to a second nucleic acid comprises
(a) providing a pair of oligonucleotide primers configured for amplifying, by polymerase chain reaction, a selected segment of the first nucleic acid and a corresponding segment of the second nucleic acid, wherein the selected segment and corresponding segment each comprises the selected locus, to result in amplified products containing a copy of the selected locus;
(b) providing a pair of oligonucleotide probes, one of the probes being labeled with an acceptor fluorophore and the other probe being labeled with a donor fluorophore of a fluorogenic resonance energy transfer pair such that upon hybridization of the two probes with the amplified products the donor and acceptor are in resonance energy transfer relationship, wherein one of the probes is configured for hybridizing to the amplified products such that said one of the probes spans the selected locus and exhibits a melting profile when the difference is present in the first nucleic acid that is distinguishable from a melting profile of the second nucleic acid;
(c) amplifying the selected segment of first nucleic acid and the corresponding segment of the second nucleic acid by polymerase chain reaction in the presence of effective amounts of probes to result in an amplified selected segment and an amplified corresponding segment, at least a portion thereof having both the probes hybridized thereto with the fluorogenic resonance energy transfer pair in resonance energy transfer relationship;
(d) illuminating the amplified selected segment and the amplified corresponding segment with the probes hybridized thereto with a selected wavelength of light to elicit fluorescence by the fluorogenic resonance energy transfer pair;
(e) measuring fluorescence emission as a function of temperature to determine in a first melting profile of said one of the probes melting from the amplified selected segment of first nucleic acid and a second melting profile of said one of the probes melting from the amplified corresponding segment of second nucleic acid; and
(f) comparing the first melting profile to the second melting profile, wherein a difference therein indicates the presence of the difference in the sample nucleic acid.
A method of detecting a difference at a selected locus in a first nucleic acid as compared to a second nucleic acid comprises
(a) providing a pair of oligonucleotide primers configured for amplifying, by polymerase chain reaction, a selected segment of the first nucleic acid and a corresponding segment of the second nucleic acid, wherein the selected segment and corresponding segment each comprises the selected locus, to result in amplified products containing a copy of the selected locus;
(b) providing an oligonucleotide probe, wherein one of the primers and the probe are each labeled with one member of a fluorescence energy transfer pair comprising an donor fluorophore and an acceptor fluorophore, and wherein the labeled probe and labeled primer hybridize to the amplified products such that the donor and acceptor are in resonance energy transfer relationship, and wherein the probe is configured for hybridizing to the amplified products such that said probe spans the selected locus and exhibits a melting profile when the difference is present in the first nucleic acid that is distinguishable from a melting profile of the second nucleic acid;
(c) amplifying the selected segment of first nucleic acid and the corresponding segment of the second nucleic acid by polymerase chain reaction in the presence of effective amounts of primers and probe to result in an amplified selected segment and an amplified corresponding segment, at least a portion thereof having the labled primer and probe hybridized thereto with the fluorogenic resonance energy transfer pair in resonance energy transfer relationship;
(d) illuminating the amplified selected segment and the amplified corresponding segment with the labeled primer and probe hybridized thereto with a selected wavelength of light to elicit fluorescence by the fluorogenic resonance energy transfer pair;
(e) measuring fluorescence emission as a function of temperature to determine in a first melting profile of said probe melting from the amplified selected segment of first nucleic acid and a second melting profile of said probe melting from the amplified corresponding segment of second nucleic acid; and
(f) comparing the first melting profile to the second melting profile, wherein a difference therein indicates the presence of the difference in the sample nucleic acid.
A method of detecting heterozygosity at a selected locus in the genome of an individual, wherein the genome comprises a mutant allele and a corresponding reference allele, each comprising the selected locus, comprises
(a) obtaining sample genomic DNA from the individual;
(b) providing a pair of oligonucleotide primers configured for amplifying, by polymerase chain reaction, a first selected segment of the mutant allele and a second selected segment of the corresponding reference allele wherein both the first and second selected segments comprise the selected locus;
(c) providing a pair of oligonucleotide probes, one of the probes being labeled with an acceptor fluorophore and the other probe being labeled with a donor fluorophore of a fluorogenic resonance energy transfer pair such that upon hybridization of the two probes with the amplified first and second selected segments one of the probes spans the selected locus and exhibits a first melting profile with the amplified first selected segment that is distinguishable from a second melting profile with the amplified second selected segment;
(d) amplifying the first and second selected segments of sample genomic DNA by polymerase chain reaction in the presence of effective amounts of probes to result in amplified first and second selected segments, at least a portion thereof having both the probes hybridized thereto with the fluorogenic resonance energy transfer pair in resonance energy transfer relationship;
(e) illuminating the amplified first and second selected segments having the probes hybridized thereto with a selected wavelength of light to elicit fluorescence by the donor and acceptor;
(f) measuring a fluorescence emission as a function of temperature to determine a first melting profile of said one of the probes melting from the amplified first selected segment and a second melting profile of said one of the probes melting from the amplified second selected segment; and
(g) comparing the first melting profile to the second melting profile, wherein distinguishable melting profiles indicate heterozygosity in the sample genomic DNA.
A method of detecting heterozygosity at a selected locus in the genome of an individual, wherein the genome comprises a mutant allele and a corresponding reference allele, each comprising the selected locus, comprises
(a) obtaining sample genomic DNA from the individual;
(b) providing a pair of oligonucleotide primers configured for amplifying, by polymerase chain reaction, a first selected segment of the mutant allele and a second selected segment of the corresponding reference allele wherein both the first and second selected segments comprise the selected locus;
(c) providing an oligonucleotide probe, wherein one of the primers and the probe are each labeled with one member of a fluorescence energy transfer pair comprising an donor fluorophore and an acceptor fluorophore, and wherein the labeled probe and labeled primer hybridize to the amplified first and second selected segments such that one of the probes spans the selected locus and exhibits a first melting profile with the amplified first selected segment that is distinguishable from a second melting profile with the amplified second selected segment;
(d) amplifying the first and second selected segments of sample genomic DNA by polymerase chain reaction in the presence of effective amounts of primers and probe to result in amplified first and second selected segments, at least a portion thereof having both the labeled primer and probe hybridized thereto with the fluorogenic resonance energy transfer pair in resonance energy transfer relationship;
(e) illuminating the amplified first and second selected segments having the labeled primer and probe hybridized thereto with a selected wavelength of light to elicit fluorescence by the donor and acceptor;
(f) measuring a fluorescence emission as a function of temperature to determine a first melting profile of said probe melting from the amplified first selected segment and a second melting profile of said probe melting from the amplified second selected segment; and
(g) comparing the first melting profile to the second melting profile, wherein distinguishable melting profiles indicate heterozygosity in the sample genomic DNA.
A method of determining completion of a polymerase chain reaction in a polymerase chain reaction mixture comprising (1) a nucleic acid wherein the nucleic acid or a polymerase-chain-reaction-amplified product thereof consists of two distinct complementary strands, (2) two oligonucleotide primers configured for amplifying by polymerase chain reaction a selected segment of the nucleic acid to result in an amplified product, and (3) a DNA polymerase for catalyzing the polymerase chain reaction, comprises
(a) adding to the mixture (1) an effective amount of an oligonucleotide probe labeled with a resonance energy transfer donor or a resonance energy transfer acceptor of a fluorogenic resonance energy transfer pair, wherein the probe is configured for hybridizing to the amplified product under selected conditions of temperature and monovalent ionic strength, and (2) an effective amount of a reference oligonucleotide labeled with the donor or the acceptor, with the proviso that as between the probe and reference oligonucleotide one is labeled with the donor and the other is labeled with the acceptor, wherein the reference oligonucleotide is configured for hybridizing to the amplified product under the selected conditions of temperature and monovalent ionic strength such that the donor and the acceptor are in resonance energy transfer relationship when both the probe and the reference oligonucleotide hybridize to the amplified product;
(b) amplifying the selected segment of nucleic acid by polymerase chain reaction to result in the amplified product, at least a portion thereof having both the probe and the reference oligonucleotide hybridized thereto with the fluorogenic resonance energy transfer pair in resonance energy transfer relationship; and
(c) illuminating the amplified product having the probe and reference oligonucleotide hybridized thereto with a selected wavelength of light for eliciting fluorescence by the fluorogenic resonance energy pair and monitoring fluorescence emission and determining a cycle when the fluorescence emission reaches a plateau phase, indicating the completion of the reaction.
A method of determining completion of a polymerase chain reaction in a polymerase chain reaction mixture comprising (1) a nucleic acid wherein the nucleic acid or a polymerase-chain-reaction-amplified product thereof consists of two distinct complementary strands, (2) two oligonucleotide primers configured for amplifying by polymerase chain reaction a selected segment of the nucleic acid to result in an amplified product, and (3) a DNA polymerase for catalyzing the polymerase chain reaction, comprises
(a) adding to the mixture an effective amount of a nucleic-acid-binding fluorescent dye;
(b) amplifying the selected segment of nucleic acid by polymerase chain reaction in the mixture to which the nucleic-acid-binding fluorescent dye has been added to result in the amplified product with nucleic-acid-binding fluorescent dye bound thereto; and
(c) illuminating amplified product with nucleic-acid-binding fluorescent dye bound thereto with a selected wavelength of light for eliciting fluorescence therefrom and monitoring fluorescence emission and determining a cycle when the fluorescence emission reaches a plateau phase, indicating the completion of the reaction. Preferably, the nucleic-acid-binding fluorescent dye is a member selected from the group consisting of SYBR(trademark) GREEN I, ethidium bromide, pico green, acridine orange, thiazole orange, YO-PRO-1, and chromomycin A3, and more preferably is SYBR(trademark) GREEN I.
A method of controlling temperature cycling parameters of a polymerase chain reaction comprising repeated cycles of annealing, extension, and denaturation phases of a polymerase chain reaction mixture comprising a double-strand-specific fluorescent dye, wherein the parameters comprise duration of the annealing phase, duration of the denaturation phase, and number of cycles, comprises
(a) illuminating the reaction with a selected wavelength of light for eliciting fluorescence from the fluorescent dye and continuously monitoring fluorescence during the repeated annealing, extension, and denaturation phases;
(b) determining at least
(i) duration for fluorescence to stop increasing during the extension phase, or
(ii) Duration for fluorescence to decrease to a baseline level during the denaturation phase, or
(iii) a number of cycles for fluorescence to reach a preselected level during the extension phase; and
(c) adjusting the length of the extension phase according to the length of time for fluorescence to stop increasing during the extension phase, the length of the denaturation phase according to the length of time for fluorescence to decrease to the baseline level during the denaturation phase, or the number of cycles according to the number of cycles for fluorescence to reach the preselected level during the extension phase.
A method of determining a concentration of an amplified product in a selected polymerase chain reaction mixture comprises
(a) determining a second order rate constant for the amplified product at a selected temperature and reaction conditions by monitoring rate of hybridization of a known concentration of the amplified product;
(b) determining rate of annealing for an unknown concentration of the amplified product; and
(c) calculating the concentration of the amplified product from the rate of annealing and the second order rate constant.
Preferably, the rate of annealing is determined after multiple cycles of amplification. One illustrative method of determining the second order rate constant comprises the steps of
raising the temperature of a first polymerase chain reaction mixture comprising a known concentration of the amplified product and an effective amount of a double-strand specific fluorescent dye, above the denaturation temperature of the amplified product to result in a denatured amplified product;
rapidly reducing the temperature of the first polymerase chain reaction mixture comprising the known amount of denatured amplified product to a selected temperature below the denaturation temperature of the amplified product while continuously monitoring the fluorescence of the first polymerase chain reaction mixture as a function of time;
plotting fluorescence as a function of time for determining maximum fluorescence, minimum fluorescence, the time at minimum fluorescence, and a second order rate constant for the known concentration of amplified product from the equation   F  =            F      max        -                            F          max                -                  F          min                                                  k            ⁡                          (                              t                -                                  t                  0                                            )                                ⁡                      [            DNA            ]                          +        1            
wherein F is fluorescence, Fmax is maximum fluorescence, Fmin is minimum fluorescence, k is the second order rate constant, t0 is the time at Fmin, and [DNA] is the known concentration of the amplified product.
A method of determining a concentration of a selected nucleic acid template by competitive quantitative polymerase chain reaction comprises the steps of:
(a) in a reaction mixture comprising:
(i) effective amounts of each of a pair of oligonucleotide primers configured for amplifying, in a polymerase chain reaction, a selected segment of the selected template and a corresponding selected segment of a competitive template to result in amplified products thereof,
(ii) an effective amount of an oligonucleotide probe labeled with a resonance energy transfer donor or a resonance energy transfer acceptor of a fluorogenic resonance energy transfer pair, wherein the probe is configured for hybridizing to the amplified products such that the probe melts from the amplified product of the selected template at a melting temperature that is distinguishable from the melting temperature at which the probe melts from the amplified product of the competitive template,
(iii) an effective amount of a reference oligonucleotide labeled with the donor or the acceptor, with the proviso that as between the probe and transfer oligonucleotide one is labeled with the donor and the other is labeled with the acceptor, wherein the reference oligonucleotide is configured for hybridizing to the amplified products such that the donor and the acceptor are in resonance energy transfer relationship when both the probe and the
reference oligonucleotide hybridize to the amplified products; amplifying, by polymerase chain reaction, an unknown amount of the selected template and a known amount of the competitive template to result in the amplified products thereof;
(b) illuminating the reaction mixture with a selected wavelength of light for eliciting fluorescence by the fluorogenic resonance energy transfer pair and determining a fluorescence emission as a function of temperature as the temperature of the reaction mixture is changed to result in a first melting curve of the probe melting from the amplified product of the selected template and a second melting curve of the probe melting from the competitive template;
(c) converting the first and second melting curves to first and second melting melting peaks and determining relative amounts of the selected template and the competitive template from such melting peaks; and
(d) calculating the concentration of the selected template based on the known amount of the competitive template and the relative amounts of selected template and competitive template.
A fluorogenic resonance energy transfer pair consists of fluorescein and Cy5 or Cy5.5.
A method of determining a concentration of a selected nucleic acid template in a polymerase chain reaction comprises the steps of:
(a) in a reaction mixture comprising:
(i) effective amounts of each of a first pair of oligonucleotide primers configured for amplifying, in a polymerase chain reaction, a selected first segment of the selected template to result in an amplified first product thereof,
(ii) effective amounts of each of a second pair of oligonucleotide primers configured for amplifying, in a polymerase chain reaction, a selected second segment of a reference template to result in an amplified second product thereof,
(iii) an effective amount of a nucleic-acid-binding fluorescent dye; amplifying, by polymerase chain reaction, an unknown amount of the selected template to result in the amplified first product and a known amount of the reference template to result in the amplified second product thereof;
(b) illuminating the reaction mixture with a selected wavelength of light for eliciting fluorescence by the nucleic-acid-binding fluorescent dye and continuously monitoring the fluorescence emitted as a function of temperature to result in a melting curve of the amplified products wherein the first product and second product melt at different temperatures;
(c) converting the melting curves to melting melting peaks and determining relative amounts of the selected template and the reference template from such melting peaks; and
(d) calculating the concentration of the selected template based on the known amount of the reference template and the relative amounts of selected template and reference template.
A method of monitoring amplification of a selected template in a polymerase chain reaction that also comprises a positive control template comprises the steps of:
(a) in a reaction mixture comprising:
(i) effective amounts of each of a first pair of oligonucleotide primers configured for amplifying, in a polymerase chain reaction, a selected first segment of the selected template to result in an amplified first product thereof,
(ii) effective amounts of each of a second pair of oligonucleotide primers configured for amplifying, in a polymerase chain reaction, a selected second segment of the positive control template to result in an amplified second product thereof,
(iii) an effective amount of a nucleic-acid-binding fluorescent dye; subjecting the selected template and the positive control template to conditions for amplifying the selected template and the positive control template by polymerase chain reaction; and
(b) illuminating the reaction mixture with a selected wavelength of light for eliciting fluorescence by the nucleic-acid-binding fluorescent dye and continuously monitoring the fluorescence emitted as a function of temperature during an amplification cycle of the polymerase chain reaction to result in a first melting peak of the amplified first product, if the selected template is amplified, and a second melting peak of the amplified second product, if the positive control template is amplified;
wherein obtaining of the second melting curve indicates that the polymerase chain reaction was operative, obtaining the first melting curve indicates that the selected first segment was amplifiable, and absence of the first melting curve indicates that the selected first segment was not amplifiable.
A method of detecting the factor V Leiden mutation in an individual, wherein the factor V Leiden mutation consists of a single base change at the factor V Leiden mutation locus as compared to wild type, comprises the steps of:
(a) obtaining sample genomic DNA from the individual;
(b) providing wild type genomic DNA as a control;
(c) providing a pair of oligonucleotide primers configured for amplifying by polymerase chain reaction a selected segment of the sample genomic DNA and of the wild type genomic DNA wherein the selected segment comprises the factor V Leiden mutation locus to result in amplified products containing a copy of the factor V Leiden mutation locus;
(d) providing an oligonucleotide probe labeled with a resonance energy transfer donor or a resonance energy transfer acceptor of a fluorogenic resonance energy transfer pair, wherein the probe is configured for hybridizing to the amplified products such that the probe spans the mutation locus and exhibits a melting profile when the factor V Leiden mutation is present in the sample genomic DNA that is differentiable from a melting profile of the wild type genomic DNA;
(e) providing a transfer oligonucleotide labeled with the resonance energy transfer donor or the resonance energy transfer acceptor, with the proviso that as between the probe and transfer oligonucleotide one is labeled with the resonance energy transfer donor and the other is labeled with the resonance energy transfer acceptor, wherein the transfer oligonucleotide is configured for hybridizing to the amplified products such that the resonance energy transfer donor and the resonance energy transfer acceptor are in resonance energy transfer relationship when both the probe and the transfer oligonucleotide hybridize to the amplified products;
(f) amplifying the selected segment of sample genomic DNA and wild type genomic DNA by polymerase chain reaction in the presence of effective amounts of oligonucleotide probe and transfer oligonucleotide to result in amplified selected segments, at least a portion thereof having both the probe and the transfer oligonucleotide hybridized thereto with the fluorogenic resonance energy transfer pair in resonance energy transfer relationship;
(g) determining fluorescence as a function of temperature during an amplification cycle of the polymerase chain reaction to result in a melting profile of the probe melting from the amplified segment of sample genomic DNA and a melting profile of the probe melting from the amplified segment of wild type genomic DNA; and
(h) comparing the melting profile for the sample genomic DNA to the melting profile for the wild type genomic DNA, wherein a difference therein indicates the presence of the factor V Leiden mutation in the sample genomic DNA.
A method of analyzing nucleic acid hybridization comprises the steps of
(a) providing a mixture comprising a nucleic acid sample to be analyzed and a nucleic acid binding fluorescent entity; and
(b) monitoring fluorescence while changing temperature at a rate of xe2x89xa70.1xc2x0 C./second.
A method of quantitating an initial copy number of a sample containing an unknown amount of nucleic acid comprises the steps of
(a) amplifying by polymerase chain reaction at least one standard of known concentration in a mixture comprising the standard and a nucleic acid binding fluorescent entity;
(b) measuring fluorescence as a function of cycle number to result in a set of data points;
(c) fitting the data points to a given predetermined equation describing fluorescence as a function of initial nucleic acid concentration and cycle number;
(d) amplifying the sample containing the unknown amount of nucleic acid in a mixture comprising the sample and the nucleic acid binding fluorescent entity and monitoring fluorescence thereof; and
(e) determining initial nucleic acid concentration from the equation determined in step (c).
A fluorescence resonance energy transfer pair is disclosed wherein the pair comprises a donor fluorophore having an emission spectrum and an acceptor fluorophore having an absorption spectrum and an extinction coefficient greater than 100,000 Mxe2x88x921 cmxe2x88x921, wherein the donor fluorophore""s emission spectrum and the acceptor fluorophore""s absorption spectrum overlap less than 25%. One illustrative fluorescence resonance energy transfer pair described is where the donor fluorophore is fluorescein and the acceptor fluorophore is Cy5 or Cy5.5.
A method for analyzing a target DNA sequence of a biological sample comprises
amplifying the target sequence by polymerase chain reaction in the presence of a nucleic acid binding fluorescent entity, said polymerase chain reaction comprising the steps of adding a thermostable polymerase and primers for the targeted nucleic acid sequence to the biological sample and thermally cycling the biological sample between at least a denaturation temperature and an elongation temperature;
exciting the sample with light at a wavelength absorbed by the nucleic acid binding fluorescent entity; and
monitoring the temperature dependent fluorescence from the nucleic acid binding fluorescent entity as temperature of the sample is changed. Preferably, the nucleic acid binding fluorescent entity comprises a double stranded nucleic acid binding fluorescent dye, such as SYBR(trademark) Green I. The temperature dependent fluorescence can be used to identify the amplified products, preferably by melting curve analysis. Relative amounts fo two or more amplified products can be determined by analysis of melting curves. For example, areas under the melting curves are found by non-linear least squares regression of the sum of multiple gaussians.